Are you supposed to be able to see the co2 cloud in the keg? I bought a 10 pound co2 tank off craigslist and I can see the cloud it left after I cleaned my keg. Is this normal?
I think the haze you are seeing is water vapour.
I assume you purged your keg with co2 to see if it would hold pressure, then you released the pressure relaese valve and took off the top. As the CO2 leaves the keg, the remaining gas gets very cold and any residual water vapour freezes into ice crystals (may be some crystals of co2 as well-dry ice)